This invention relates generally to nanoscale fibers, and more particularly to electromagnetic interference (EMI) shielding structures comprising nanoscale fibers.
Due to the growing need for more powerful and compact electronic products, EMI is becoming a more significant factor in commercial and military applications. The EMI shielding of electronic devices and/or radiation sources may be a consideration in the reliable operation of devices, and possibly in preventing human health risks.
Thin film attachment or spray coating of metal, conducting polymers, and carbon black particles on a product surface may shield the product from electromagnetic waves. Metal serves as an effective shielding material because of its high conductivity, but metal adds significant weight and corrosion issues. Conducting polymers and carbon particles are lightweight but their conductivity is not as high as that of metal. Carbon nanotubes may offer an alternative for EMI shielding due to their light weight, corrosion resistance, and high conductivity (˜106 S/cm).
Carbon nanotube (CNT) thin films, or buckypapers (BPs), are highly conductive, lightweight materials that are easily incorporated into structural composites. These properties make BP use in EMI shield/structural multifunctional composites an attractive option. Single-walled carbon nanotube (SWNT) BP can provide high EMI shielding because of its high electrical conductivity. Since mixed SWNT and multi-walled carbon nanotube (MWNT) or carbon nanofiber (CNF) BP also has high conductivity and is lower in cost, it could also be used for EMI shielding.
Present carbon nanotube based composite techniques are sometimes based on mixing nanotubes with resin. However, such methods can fail to achieve high nanotube loading and high conductivity in composites, which would be desirable for EMI shielding. To increase the electrical conductivity and mechanical properties, higher loading of CNTs in composites is desirable. However, CNT composites made by mixing CNTs with a polymer matrix are difficult to achieve high CNT loading (i.e., >10 wt. %). Higher loading will lead to high viscosity and agglomeration of the CNTs, thus undesirably decreasing the mechanical properties and quality of the composites.
It would therefore be desirable to provide improvements in EMI shielding structures having nanotubes and/or nanofiber films. In particular, it would be desirable to provide improved EMI shielding structures that may be produced in a relatively lightweight form and at a relatively low cost. It also would be desirable to provide improved methods for producing EMI shielding structures that include nanotubes and nanofiber films.